Heat treatment of glass textiles



Patented Nov. 18, 1941 Howard B. Lillie and Eric H. Loytty,

N. Y., assignors, by mesne assignments, to

Owens-Corning Fiber notation of Delaware glas Corporation. a cor- No Drawing. Application June 24, 1938,

- Serial No. 215,688

5 Claims.

number of fibres of this nature are twisted together to form a thread and subsequently woven or knitted into a textile fabric, neither the thread nor the fabric has a strength commensurate with the sum of the strengths of the individual fibres contained therein. This is believed due, at least in part, to lack 'of parallelism of the fibres, the stresses set up in the individual fibres as they are bent over and under one -an-- other, and, further, to the abrasion of the fibres at these points of contact, both increasing the tendency for fibres to break and thereby lowering the efiiciency of the fabricated material as compared with the individual fibres.

When yarns and fabrics composed of glass fibres are immersed in liquids, particularly water, or used in humid atmosphere, a marked decrease from their corresponding dry strength occurs. This is believed partially due to the tendency of water to combine with and leach out the alkali content of the glass which tends to attack the remainder of the glass, actually reducing the diameter of the fibres and eventually cementing them together at their points of contact, thereby decreasing the ability of the fibres to slip past one another and increasing the abrasion at these points However, an almost equaly high loss in strength occurs when fabrics of a lowalkali or alkali-free glass composition are wet. This can the dry and particularly treating the fibres, preferably after fabrication, at a relatively low temperature for a limited period of time, More specifically, an increase in the wet strength of glass fibres and fabrics made therefrom of up to 150%, depending on the humidity conditions under which the test is made, may be obtained by heating low alkali and alkali-free fibrous glass products for a period of from one to thirty minutes at a temperature of from 50 C. to 340 C. This treatment may take place at any time after the formation of the fibres, but preferably after the fibres have been fabricated into yarn or cloth, and will produce beneficial results whether the fibres are in their original oil-free condition or have been lubricated. Heating may be accomplished either intermittently by operating on sepate quantities of finished material or continuously as by passing the fabric through a rially increased, both in in the wet state, by heat heating furnace of proper type and temperature possibly be accounted for either on the theory that the moisture tends to reduce the efficacy of the lubricants applied to glass fibres or that the moisture is drawn into the surface flaws known to exist in glass of all descriptions, thereby changing the force of attraction between the mirror surfaces of the flaw which, in the case of a very fine fibre, may make a major change in the strength ofthe fibre at that point.

Whatever the reasons for the loss of strength in glass fibres, yarns, and fabrics when wet, it has been found that the strength of glass fibres and fibrous glass products made from low alkali as it comes from the loom or knitting'machine. The glass compositions referred to above are those in which the total alkali metal oxides do not exceed 3% of the glass composition.

Inasmuchas the precise reasons for loss of strength by fibrous glass products when they are wet are not fully known, the effects of heat treatment cannot be stated completely and exactly. It is known from experimentation that the strain release temperature of glass fibres of very fine diameter is materially lowered due to the rapidity with which they are cooled. This may amount to as much as 300 C. bringing the strain release temperature for a glass fibre as low as 200 0., approximately. While the total amount of strain release occurring at a given temperature depends om the particular glass composition and the period for which it is held at that temperature, it has been found that values of 25% and more can be obtained with most glasses when heated at as low a temperature as 200 C. for from five to thirty minutes. When woven or knitted glass fabrics are 'heat treated in this manner, it is found that a permanent undulation is set in each thread which corresponds to its position in the fabric, whilethe tendency of a thread to untwist is substantially eliminated. Thus, one definite effect of heat treatment of fibrous glass textiles is to reduce the strain set up in the fibres by their fabrication into textiles and produce a stronger fabric whose threads have less tendency to slide on one another andunravel.

Further advantages are derived from heat and alkali-free glass compositions can be matetreatment as tests of single fibres show, but the reasons therefor are obscure. While strain release takes place equally well' with low alkali.

glasses and those having a large percentage of NazO in their composition, only those glasses which are substantially free from or have less than 3% of alkali metal oxides in their composition show an actual increase in strength in individual fibres due to heat treatment. This increase is observed both with oil-free and lubricated fibres, yarns, and fabrics, although it is more pronounced when an oil is present on the surface of the fibres during heat treatment. Furthermore, the change in strength varies with the temperature at which the fibres are treated. Thus, with a representative glass containing approximately 2% of lithia, the strength of fibres and textiles after heat treatment is found to increase uniformly with the treating temperature used up to and including 200 C., after which it gradually decreases reaching its original value after treatment at 340 C. and having but half its original strength after treatment at 450 C.

The increase in strength effected by heating at a given temperature has been found to vary with humidity, increasing proportionately with increase in humidity, and to be more pronounced with the lighter weights of fabricated materials. By way of illustration, the following tables are given showing the strength in pounds of 1 and 2 grain yarn made from fibres of the representative glass referred to above both plain and heat treated at 200 C. for one-half hour.

Thus it will be seen that -ina dry atmosphere the increase in'strength of a heat treated, oiled yarn over the same yarn in its regular condition may be only about 2%, while under conditions of 100% relative humidity the heat-treated yarn may have a strength as much as two and onehalf times that of the regular yarn. Stated in a different way, the wet strength of a heat treated yarn may be from 65% to 75% of its dry strength, while the wet strength of a regular these weights-of yarn are heat treated.

It is believed that part of the above effect may be due to a tougheningand baking-on of the oil film which seals surface fiaws in the fibres and generally renders them water resistant, but this can be only part of the effect produced for a similar, though less pronounced effect is obtained by treating oil-free yarns and fibres. For example, an oiled yarn of low alkali glass fibres has been observed to lose 30% of its strength as the relative humidity of the surrounding atmosphere increases from 47% to 70%. Under the same conditions, an oil free yarn which lost 20% of its strength before being heat treated lost only 11% of its strength after heat treatment. After heat treatment the oiled yarn lost only 1% of its strength with the same change in humidities. In all of the above cases the heat treatment of the yarn was carried out at 200 C. for one half hour.

While certain specific treatments of various fibrous glass products and the results obtained thereby have been described in some detail, such description is by way of illustration, rather than of limitation and the present invention is to be limited solely by the scope of the following claims.

We claim:

1. The method of making glass textile material having a high wet strength which comprises forming filaments from a glass containing up to 3% of alkali metal oxides, fabricating said filaments into a textile material, and heating said material at a temperature between 50 C. and 340 C. for a period of from 5 to 30 minutes.

2. The method of making glass textile material having a high wet strength which comprises forming filaments from a glass containing up to 3% of alkali metal oxides, fabricating said filaments into a textile material, and heating said material at a temperature between 50 C. and 340 C. for at least five minutes.

3. The method of making glass textile material having a high wet strength which comprises forming filaments from a glass containing up to 3% of alkali metal oxides, coating said filaments with a lubricant, fabricating said filaments into a textile material, and heating said material at a temperature sufficiently high to remove a portign of said lubricant, but not in excess of 340 C.

4. The method of making glasstextile material having a high wet strength which comprises forming filaments from a glass containing up to I yarn may be only 30% to 34% of its dry strength. Similar effects are found when'fabrics made from 3% of alkali metal oxides; coating said filaments with a lubricant, fabricating said filaments into a textile material, and heating said material at a temperature sufiiciently high to remove a portion of said lubricant, but not in excess of 340 C. for a period of at least five minutes.

5. The method of making glass textile material having a high wet strength which comprises forming filaments from a glass containing up to 3% of alkali metal oxides, coating said filaments with a lubricant, fabricating said filaments into a textile material, and heating said material at a temperature of 200 C. for aperiod of thirty minutes.

HOWARD R. LILLIE. ERIC H. LOY'I'I'Y. 

